1. Field of the Invention
This invention relates to injection-molded and extruded tampon applicators and in particular to injection-molded and extruded tampon applicators which are water-dispersible and biodegradable. More specifically, the invention relates to injection-molded and extruded tampon applicators made from a modified poly(vinyl alcohol) which is self-plasticizing.
2. Description of the Art
The standard construction for a tampon applicator is a pair of telescoping tubes, the outer tube carrying the tampon's absorbent material (the tampon's "pledget") and the inner tube serving as a plunger for dispensing the pledget. Tampon applicators in current commercial use are typically made from either a plastic or paper-based material. Plastic tampon applicators are preferred by many women since they can be molded to include a grip ring and a petal-shaped forward end which aids in the insertion of the device and in retaining and protecting the pledget while it is in the outer tube. Plastic tampon applicators are typically made from polyethylene using an injection-molding process.
A convenient place to dispose of a tampon applicator is in a toilet bowl, even though all of the currently used plastic applicators are ill-suited for such disposal. While such applicators will flush, they settle in septic tanks without decomposing. Moreover, they accumulate on the screens in waste-water treatment plants, creating blockages. If the screens don't stop them, they escape into the environment intact, often washing up on beaches. Because plastic tampon applicators typically neither float on the surface nor settle to the bottom of settling tanks, they are not removed as sludge or by skimmers. In view of such environmental and esthetics considerations, it is thus highly desirable that the plastic applicator be water-dispersible and biodegradable. Such properties have not yet been achieved commercially, in spite of efforts to achieve these properties for a plastic-based material which have been on-going for at least the past forty years.
An early patent in this area is U.S. Pat. No. 2,518,486 to William Mende. Although not specifically a tampon applicator, the Mende patent describes a device for dispensing pharmaceutical preparations into body cavities which includes an outer tube and a plunger. To avoid problems with clogging of toilets, Mende suggests forming his device from a synthetic material which will soften and swell upon contact with water, such as a poly(vinyl alcohol).
U.S. Pat. No. 3,882,869 to David Hanke discusses Mende's poly(vinyl alcohol) proposal and concludes that Mende's approach is unworkable in a commercial environment because the poly(vinyl alcohol) becomes unstable in the presence of moisture laden air, becomes prematurely sticky in contact with moist surfaces, and is costly to fabricate since it must be cast from solution and then molded to shape (see Hanke at column 1, lines 48-59). As an alternative to Mende's approach, Hanke suggests using a polyethylene oxide polymer or hydroxypropyl cellulose containing between about 50 and about 75 percent by weight of a filler such as talc.
In another of his patents (U.S. Patent 3,724,462), Hanke discloses a further approach for using water-soluble polymers in the preparation of tampon applicators. In accordance with this patent, the inner and outer tubes of the applicator are made of different water-soluble polymers which are incompatible with one another. In this way, problems with the tubes fusing together under high humidity/high temperature conditions are avoided. Poly(vinyl alcohol) polymers were again studied in this patent and it was observed that this polymer developed a sticky surface when subjected to a temperature of about 120 degrees F (about 49 degrees C) and a relative humidity of about 90 percent.
In addition to being sticky, tampon applicators made from poly(vinyl alcohol) polymers also suffer from odor problems; specifically, they can have an acetic acid smell. Hanke U.S. Patent Nos. 3,911,917 and 3,882,196 address this problem by mixing a proton acceptor such as calcium carbonate with the poly(vinyl alcohol) polymer before the polymer is injection molded to form the applicator.
A recent patent application in this area is South African application Serial No. 87/3135 to Carlton Paper of South Africa, Limited. This application describes the injection molding of a mixture of partially hydrolyzed poly(vinyl alcohol) (80 percent by weight) and a plasticizer (20 percent by weight) to produce tubes for tampon applicators. Poly(vinyl alcohol) cross-linked with an aldehyde is described as an alternative material but was not employed in either of the two examples.
The need for 20 percent by weight plasticizer shows that the hydrolyzed poly(vinyl alcohol) used by Carlton Paper was not truly a thermoplastic resin. Also, the use of a plasticizer at these levels can be expected to result in increased moisture sensitivity, decreased tensile strength, and migration of the plasticizer from the finished product so as to produce a slimy or slippery outer surface. In addition, as is typical of conventional poly(vinyl alcohol)s, Carlton Paper's device exhibited a slow dissolution rate in cold water. Specifically, Carlton Paper reported in its South African application that 16 hours were required to dissolve a hollow tube of its externally-plasticized material in cold water. The tube had a wall thickness of one millimeter.
Poly(vinyl alcohol) polymers are also suggested for use in tampon applicators in Potts' U.S. Pat. No. 4,372,311. This patent discloses a two-layer material wherein a watersoluble polymer, e.g., a poly(vinyl alcohol), is coated with a non-water soluble, but biodegradable, polymer, e.g., a polycaprolactone.
Examples of efforts to use materials other than poly(vinyl alcohol) to manufacture tampon applicators which are water-dispersible and/or biodegradable can be found in Kraskin et al., U.S. Pat. Nos. 3,954,104 and 4,099,976 (hydroxyalkyl cellulose) and in European Patent Publication No. 291,024 [poly(3-hydroxybutyric acid)].